Excavations and Foundations

Question 1

What is setting out?

Answer 1

Transferring details of positioning of building from a drawing onto the site

Question 2

What is a theodolite?

Answer 2

It consists of a telescope mounted to swivel both horizontally and vertically to determine horizontal and vertical angles.

Question 3

Name 5 different types of earth moving

Answer 3

Site clearance

Stripping topsoil

Reduced level dig out to reach formation level for the start of construction

Cut and fill operations where site levels vary

Bulk excavation – generally for basements

Question 4

What is the function of foundations?

Answer 4

To transfer all loads (dead, live and superimposed) from the building to the ground with sufficient bearing capacity.

Question 5

What factors effect the choice of foundation?

Answer 5

The total loads of the building;

Nature and bearing capacity of the subsoil; and

The amount of settlement produced by the loading

Question 6

What are the different types of loads on a building?

Answer 6

Dead Load: all the materials in the structure

Live load: people using the building and the furniture

Superimposed loads: wind, snow etc.

Total load: summated from the above.

Question 7

What are the different types of shallow foundations?

Answer 7

Strip

Pad / deep strip / trench fill

Raft

Question 8

When might strip foundations be suitable?

Answer 8

When light loadings are imposed on reasonable strong soils. Typically used in low rise residen

Question 9

What approved document relates to foundations?

Answer 9

Part A

Question 10

When might wide strip foundations be suitable?

Answer 10

Strip foundations on subsoils with poor bearing capacity, such as soft sandy clays, may need to be considerably wider than the wall they support to spread the load to a sufficient area of subsoil for stability.

Question 11

Where are raft foundations used?

Answer 11

Used where the soils bearing capacity and the buildings structural loading is low. Where differential settlement is likely.

Question 12

Where are pad foundations used?

Answer 12

They are more common on larger purpose built structures such as industrial units or other commercial buildings to support large roofed structures

Question 13

When are shallow foundations used?

Answer 13

Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils. Deep foundations (more than 3 m from the surface) may be necessary where the bearing capacity of the surface soils is insufficient to support loads imposed.

Question 14

What are pad foundations?

Answer 14

Pad foundations are rectangular or circular pads used to support localised loads such as columns

Question 15

What are raft foundations?

Answer 15

The foundation becomes a large reinforced concrete slab covering the whole area of the building and constructed just below the surface of the ground

Question 16

What are piles foundations and when might they be suitable?

Answer 16

Piles are a series of columns constructed or inserted into the ground to transmit the loads of a structure to a lower level of subsoil. These are a type of deep foundation, typically used where the earth close to the surface does not have sufficient load bearing capacity and the building load therefore need to be transferred to load bearing strata at a greater depth.

Question 17

What the main types of pile and what are the main difference?

Answer 17

Replacement and displacement. Replacement piles are excavated using an auger, removing arisings and infilling with in-situ cast concrete columns. Displacement piles are formed of either pre-cast concrete of streel columns which are driven into the ground, displacing the earth around them.

Question 18

What is a ground beam?

Answer 18

Reinforced concrete ground beams connect piles and are a very efficient method of providing foundation support to new structures built on poor ground, particularly beneath continuous masonry walls.

Question 19

What are pile caps?

Answer 19

Piles can be used individually, or they can be grouped together and linked by a reinforced concrete cap. Pile caps create a stable foundation and offer a larger area for the distribution of the building load onto the piles.

Question 20

What is the difference between replacement and displacement piles?

Answer 20

Replacement:

• Cohesive soils
• Arisings (excavated soil)
• Vibration free
• Noise free

Displacement:

• Granular soils
• No arisings
• Vibration of ground
• Noisy